Fibrous cellulose esters, particularly cellulose acetate, are the commercially preferred media for filtration of smoke from filtered cigarettes. This commercial application consumes worldwide several hundred million pounds of cellulose acetate fiber per year. During the production of these filtered cigarettes, a certain percentage of them will not be brought to market, due to damage of goods, variation from specifications, or other reasons. Those cigarettes which are not sold are typically subjected to a reclamation process wherein the tobacco-laden portion of the cigarette is mechanically broken from the filter, and the tobacco is removed by shaking within a screening device. An example of this process is given in U.S. Pat. No. 3,224,451, which is incorporated herein by reference. After reclamation of tobacco, several tens of millions of pounds of residual material, referred to as "ripper waste" in the industry, comprised of cellulose acetate (typically plasticized for example with glycerol triacetate), paper, residual tobacco, and often flavors and fragrances remain; this ripper waste is most generally disposed of as landfill, representing both a loss of natural resources and a burden on landfill capacity.
The composition of "ripper waste" varies depending on the specifics of the cigarette products and the tobacco reclamation process employed. Typical composition ranges, by weight, of ripper waste are: a) cellulose acetate, 40-55%; b) plasticizer, 1-12%; c) paper, 25-45%; d) residual tobacco, 1-15%; e) adhesives, 2-3%; and f) flavors/fragrances, &lt;1%. Additional components for example charcoal, may be found in these waste streams, depending on the specific cigarette product.
The physical/mechanical separations employed in reclaiming cigarette components have in the past either focused on sifting tobacco away from other components, as is the case in U.S. Pat. No. 3,224,451, or in the removal of cellulose acetate filter media from its paper liner, as in U.S. Pat. No. 4,261,790, which is incorporated herein by reference. Other approaches have included enzymatic degradation of the cellulose acetate to produce useful sugars, as in U.S. Pat. No. 4,298,013.
Isolation of cellulose acetate from "ripper waste" is insufficient to provide a recycled product of high commercial utility. During the manufacture of cigarettes, the cellulose acetate is treated with a plasticizer which improves the mechanical performance of the finished filter. The cellulose acetate may also be treated with flavorants, for example, menthol, and the cellulose acetate will absorb some levels of nicotine and other substances from the tobacco. If the cellulose acetate/plasticizer/flavors mixture is dissolved in a typical cellulose ester solvent, and reformed into a product, these extraneous substances will change both the mechanical and the sensory properties of the cellulose acetate, thereby reducing the overall quality of products manufactured with these recycled materials. Extraction with conventional solvents, such as ethanol, can be used to remove the majority of undesirable contaminants from cellulose acetate. But, the extraction solvents then becomes an undesirable contaminant, and reduces the product quality. An additional difficulty introduced by use of such extraction solvent is that they can escape into the environment, necessitating costly preventative measures.
Supercritical and near supercritical fluids have previously been described for the extraction of: removal of adhesives from cellulose (See, U.S. 5,009,746); terpenes and oils from wood (See, U.S. Pat. No. 4,308,200); lignin from Kraft streams (See, U.S. Pat. No. 4,493,797); and removal of the natural oils from plant matter (See, U.S. Pat. No. 4,675,198). Commercial applications of this technique include: the decaffination of coffee and tea; extraction of hops flavors for beer manufacture; and denicotination of tobacco. Such commercial processes are well known to those skilled in the art and are described in reviews such as: McHugh and Krukonis, Supercritical Fluid Extraction: Principles and Practice, Butterworths; (1986); Eckerd et al., Environmental Science and Technology, Vol. 20, pp. 319-325, (1986); "Supercritical Fluids", Kirk-Othmer Encyclopedia of Chemical Technology 3rd, John Wiley & Son, New York, each of the foregoing are incorporated herein by reference.
While the supercritical extraction of natural products from cellulose is described U.S. Pat. No. 5,009,746, it does not describe the removal of polymeric additives and impurities from cellulose acetate. Those familiar with the chemistry, binding properties, and solution properties of both cellulose acetate and cellulose will recognize that these two structural polymers share few common properties, and, therefore, must therefore be treated as different materials. See, "Cellulose" and "Cellulose Acetate" Kirk-Othmer Encyclopedia of Chemical Technology 3rd, John Wiley & Sons, New York, both of which are incorporated here in by reference.